It is generally believed that controlling the compressor on/off cycles by directly determining the temperature inside the refrigeration compartment may impair correct cyclic defrosting of the evaporator.
Locating a temperature sensor (electronic or mechanical—the latter in the form of an expansion bulb) directly on the evaporator, when the thermostat (electromechanical or electronic) is normally located inside the refrigeration compartment, normally on the lighting fixture of the refrigeration compartment, obviously poses numerous manufacturing and assembly problems resulting in a relatively high production cost of the end product (appliance).
The same problem of ensuring defrosting of the cooling means, albeit to a much lesser extent, also arises in the case of refrigeration compartments cooled using a Peltier-effect solid-state electronic device, which, however, is much more expensive and therefore cannot be used in ordinary electric household appliances.